The configuration of piping systems is complex in alternative fuel vehicles. The fuel, either natural gas or hydrogen, is normally stored in a high pressure tank, controlled by solenoid gas valves when it is in operation. Generally, the space in a vehicle is limited; hence a small size of valves and piping systems is desired. In addition, having an in-line inlet and outlet ports would simplify the arrangement of piping systems.
Valves are used to control the flow rate of the fuel under a specified inlet pressure. Because of the inlet pressure restrictions and temperature variations, it is difficult to design an appropriate valve that meets all the requirements for the piping systems. Solenoids of a reasonable size can typically produce a pulling force that is approximately only 1/100 of the force necessary to unseat a valve that is being forced shut by the high-pressure gases. To overcome this, most of the gas valves adopt a two-stage process in which a small “bleed” orifice is first opened, allowing the high-pressure gas from the storage tank to flow into a downstream outlet passage way through the “bleed” orifice that leads to the engine. As the downstream outlet passage way filled with gas, the pressure will increase, subsequently reducing the force necessary gradually to unseat the closed valve. Eventually, the differential pressure between the upstream and downstream passage ways becomes infinite small to allow the valve to be opened by a relatively weak pull of the solenoid valve, thus resulting in the flow of high-pressure gas from the storage tank to the vehicle engine.
In a typical two-stage valve assembly, two pistons were required in the operation solenoid assembly, namely primary piston and main piston. The primary piston is located on top of the main piston. When in operation, the primary piston is first opened to allow gas flow through a small bleed orifice located on the main piston to create a pressure difference between the front and back sides of the main piston. This difference in pressure causes the valve to open to gain full gas flow. Since the movement of both pistons affects one another, the opening stroke (distance) of the primary piston must be equal to or larger than that of the main piston to give required operations. Since an electrical coil is utilized to generate magnetic field to cause the primary piston to open, the longer the primary piston has to travel, the less magnetic force the piston experiences. This becomes problematic if the pressure of the inlet is increased. Hence, to increase the magnetic attraction force that the primary piston experiences, the magnetic field strength has to be increased. To increase the magnetic strength, the number of turns of the electrical coil has to be increased if the input current stays the same. An increase in number of turns in a coil also increases the size of the solenoid assembly, which is undesirable.
In the current design, described hereafter, the equivalent main piston will move with a solenoid assembly while the movement of equivalent small piston does not affect the movement of the main piston. It can reasonably reduce the size of valve and/or increase the gas flow rate.